You can start learning piano right now. Just make the decision and then start practicing. You are a piano player the moment you step onto the path of what I call the piano journey. The key to progressing, growing, building skills, and developing into a confident and competent piano player is to stay on the path... never give up.
The path to learning piano is a long one, full of many details to learn and many skills to master. But anyone who has the desire and motivation can do it. You just need to make sure you are ready to enjoy every step. If you are not prepared to find pleasure in the "small" things, the nitty-gritty details, you are likely to become overwhelmed with frustration and impatience.
From the very beginning, be determined not only to accept the work but also to take pleasure in the work. As a beginner, you cannot expect beautiful piano music to be flowing out of your piano any time soon. That comes a little further down the path. So enjoy the other things: teaching your fingers to play independently; developing "keyboard awareness" in your hands and in your mind; producing solid tone; a growing feel for the piano keys; learning new skills and knowledge; becoming a musician.
Enjoy the journey, or you may loose the desire to continue on the journey.
Somewhere along the way, you may want to read "Piano Player... You", as it will give you a solid overall picture of your piano journey. Many have already found it to be an excellent guide for their piano odyssey.
The best way to start learning piano is to start playing. I have assembled 17 familiar tunes for beginners to learn, arranging them in order of progressing difficulty (none of them are too difficult for a beginner). With each tune you will find a video, piano tab (the notes and fingerings written for non-music readers), and the actual music notation. Every tune is presented in 3 different keys (so the new pianist begins to learn how to move a tune to different positions on the piano).
Prior to learning these tunes, you will need some basic stuff first, so go through lessons 1-3 before tackling any of the rest:
Lesson 3: Mary Had A Little Lamb in C, F, & G
Lesson 4: Twinkle, Twinkle Little Star in C, F, & G
Lesson 5: When The Saints Go Marching In in C,F, & G
Lesson 6: You Are My Sunshine in C,F, & G
Lesson 7: Down In The Valley in C,F, & G
Lesson 8: Frere Jacques in C,F, & G
Lesson 9: Alouette in C,F, & G
Lesson 10: Yankee Doodle in C,F, & G
Lesson 11: The Water Is Wide in C,F, & G
Lesson 12: Brahms Lullaby in C,F, & G
Lesson 13: Home On The Range in C,F, & G
Lesson 14: Danny Boy in C,F, & G
Lesson 15: Amazing Grace in C,F, & G
Lesson 16: Simple Gifts in C,F, & G
Lesson 17: America the Beautiful in C,F, & G
Lesson 18: The Star Spangled Banner in C,F, & G
Lesson 19: Greensleeves in A-minor, D-minor, & E-minor
-Click here for a series of simple exercises that will help you begin to develop some basic piano technique, keyboard awareness, and just a general feel for the keys.
I use these two "tunes" more extensively as a part of exercises with my students. They are excellent tools for the developing pianist: